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UNIT 4
ANIMAL POPULATIONS
4.1 POPULATION DYANAMICS
Population dynamics describes constant changes in:
1.Size
•increased growth comes from births and immigration;
•decreases come from deaths and emigration.
•Carrying Capacity
 It is the maximum population that a habitat can support over a
given time period.
 Size is limited by availability of resources and niches
 Population growth slows as K is reached.
•Technological, social and other cultural changes have extended
human’s range - but how long will it last?
• S-Curve Growth
 either indicate growth
with fluctuations
above and below K,
 or cyclic growth
where the rate
changes as the
population increases.
• J-Curve Growth
 indicate exponential
growth where
populations overshoot
resources and crash;
also called irruptive;
 has random spikes
and crashes.
 The problem is that
early growth curves
may look like S when
they are actually J.
• Populations are limited in their
capacity for growth in two
ways:
a. R-strategists: (R=reproductive
potential)
• These species have high
birth rates; little parental
care, reproduce quickly;
and have cyclic growth
rate
• ex: rodents, insects
b. K-strategists: (K= carrying
capacity)
• These species have low
birth rates; high parental
care; mature slowly; and
have stable growth rate
• ex: large mammals
2. Density
• is the number of
species per habitat
space.
• Dense populations
tend to have lower birth
rates and higher
disease rates.
• However, this tends to
bring high populations
back down.
• There is controversy
over whether predators
actually control the
density of the prey, or
vice versa.
• Density independent factors are climate, natural
disaster and growth requirements.
• Density dependent facts are competition, migration,
predation and symbiosis.
3. Dispersion - uniform or random distribution, or
clumping of populations due to availability of
resources or niches
4. Age distribution is based on how many individuals
are reproductive and how long they stay that way.
Show in survivorship curves or age structure
histograms.
• A survivorship curve
indicates trends in
populations related to the
number of individuals at
each age
a. late loss - living long after
reproductive age. ex:
humans
b. constant loss - deaths are
about equal at all ages. ex:
birds
c. early loss - fish have short
life cycles, but are
reproductive most of their
life
4.2 NATURAL SELECTION
1. Populations change
because of adaptations to
• the environment
• natural selection
• Mutations.
2. Speciation is the
formation of new species
from an older species.
3. Speciation - extinction =
biodiversity.
4. 3 kinds of
Adaptations:
• Morphological specialized structures
for habitat,
camouflage ex: ducks
with webbed feet
• Physiological specialized functions.
ex: venom in spider
• Behavioral migration, mimicry
like these wings with
“eyes”
Hardy-Weinberg Law of Population
Genetics.
The Law lists criteria that would have to
happen for the gene pool NOT to
change.
1. Mating would have to be random.
2. There could be no mutations.
3. There could be no immigration
(entering) or emigration (exiting) an
ecosystem so the number of genes
remained constant.
4. Populations would have to be large
because the Law of Probability is
more accurate when the sample is
large.
• Since all of these criteria can never be
met, change will occur.
New species arise from:
1. Geographic isolation - a small
group separated from the
main population will rotate
only a few genes. ex: a canyon
separates squirrels and a new
specie develops
2. Reproductive isolation - some
birds show a preference for
particular colors, dances or
displays.
3. Adaptive radiation species move out of
home range like the
finches
4. Convergence different species in
same habitat develop
similar
characteristics.
– ex: fish and whales
5. Co-evolution adaptations based on
dependence to
another organism.
– ex. clownfish and
anemone
Natural Selection
Results when individuals best
suited to the environment are
able to survive.
3 types of natural selection:
1. Directional selection
• entire population moves
toward an extreme
• ex: giraffes with longer
necks survive better
2. Stabilizing selection
• survival favors being average
• ex: large mice may need too much food, and have
trouble hiding; tiny mice may be too weak to find
food - being average-sized might be better
3. Diversifying selection –
• extremes are better able to
adapt
• ex: gray peppered moths did
not blend with the
environment; black and
white moths had an
advantage during the
Industrial Revolution
because they matched
buildings better
• Mutations are random
genetic accidents; may be
beneficial or harmful but
they change the
population’s characteristics.
4.3 AMPHIBIANS
AMPHIBIANS & THE ENVIRONMENT
1. Amphibians are an indicator species
who have survived for 350 million
years.
2. This long history indicates their
adaptability to environmental
changes.
3. Their decline on every continent
where they live, suggests declining
environmental health.
4. Fossil records indicate 10 different
Amphibian Orders, whereas today
there are only 3 Orders. Frogs,
toads, and salamanders compose
two Orders and the third contains
the worm-like caecilians.
5. The most common frog was
Rana pipens, the Leopard frog.
6. Amphibian populations are
declining due to:
• increased UV radiation from
ozone depletion
• chemical poisoning from
pesticides and fertilizers
• acid rain
• competition from predators
and exotics
7. Humans have altered the
environment so that predators
and exotics have access to new
habitats and compete with frogs
both as predators and for prey.
8. Class Amphibia is
important to ecosystems
because they are used
for prey by other species
and have commercial
value as medicine.
9. Contrary to legends,
warts are from viruses not frogs or toads.
AMPHIBIAN LIFE CYCLE
1. The word Amphibian means double life. They
must spend part of their life in the water and part
on land. Generally, the larvae remain in water,
while adults live on land.
2. All Amphibians must return to the water for
reproduction. Their egg has no shell and is part of
a jelly-like mass that must be kept moist.
3. The eggs are dark on the
top half and light on the
bottom half. Larvae have
a round, heavy-looking
body with a thin tail.
4. As metamorphosis
continues, the tail is
reabsorbed and hind
legs appear. Front
appendages appear
shortly before the
tadpole becomes an
adult.
5. Tadpoles are herbivores.
6. Adults eat insects and
small lizards.
GENERAL CHARACTERISTICS OF AMPHIBIANS
1. Moist skin - can exchange gases through the skin
2. Two nostrils - connect to the mouth and lead to the
lungs
3. Adults use lungs for respiration, while larval stage has
gills.
4. Three-chambered heart and cold blooded circulation
5. Delicate, bony skeleton
6. hibernate in burrows in
cold weather; aestivate
to escape summer heat
or drought
7. many are nocturnal
8. life-span between 4-15
years for toads
4.4 FATAL SUBTRACTION
IMPORTANCE OF WILD
SPECIES
1.Wild species are
important for their
economic, medical,
scientific, ecological,
aesthetic, and recreational
value.
2.Wild tropical plants
provided 90% of today’s
food crop seeds; 80% of
medicines came from
plants that were wild.
Hyacinth Macaw
3. Bioethics is the right of any species to exist. The
average specie lasts about 4 million years.
4. Background (normal) extinction rate is about 3
species per year. Currently, it is 1000 times that
amount.
CAUSES OF SPECIES
DECLINE
1. habitat loss or fragmentation
(primary factor)
2. human population growth
3. pest and predator control
4. harvesting wild plants
5. hunting, fishing, poaching
6. for sale to collectors and as
exotic pets
7. pollution and related
diseases
8. exotics have altered habitat
giving other species new
advantages
3 LEVELS OF DECLINING POPULATIONS
1.Local Decline - no longer found in one native area
but are found elsewhere in the world.
2.Ecological Decline - specie is present but can’t
play its role in the ecosystem
3. Biological Decline
a. Threatened - declining in
numbers
b. Endangered
•
•
too few individuals, extinction
soon
Species need 10,000
organisms to maintain
evolutionary potential.
c. Extinct
•
•
means gone forever - when
numbers drop below 1,000 for
animal species and 120
species for plants
the species is considered
extinct because of the
problems finding mates.
• Populations are doomed
when the death rate is
greater than the birth rate.
• These organisms have
fallen below their minimal
viable population size.
• They will become extinct
unless change occurs
somewhere.
4.5 ENDANGERED SPECIES
ENDANGERED SPECIES ACT (1973)
1.“Conserve and restore endangered and threatened
species and the ecosystems upon which they depend.”
2.It requires protection for any endangered or
threatened species take precedence over economic
concerns.
3.The Department of the Interior, acting through the
U.S. Fish and Wildlife Service (FWS), is responsible for
protecting most threatened and endangered species.
4. The number of endangered and
threatened species went from 92
to 963 between 1973 and 1995.
5. Then, from 1995 to 1996, Congress
banned any more listings.
6. Only 21 species have recovered
enough to be reclassified to
threatened and 11 species have
been recovered enough to be
removed from the list.
7. However, 40% of the species are
stable or improving.
8. The ESA has been unpopular with industry, developers,
miners, and timber ranchers, who contributed nearly $1
million to support repealing it.
9. However, the ESA has had no negative impact on U.S.
economic development.
10. Funding costs each adult about 25 cents per year.
The Number of Endangered Species by Vertebrate
Class and Most Affected Specie in Each Group
OTHER TREATIES & LAWS
1.Migratory Bird Treaty Act
• prevent the destruction of
non-game migratory birds or
eggs.
• considers some 170 species
to be “game birds,” less than
60 species are typically
hunted each year.
• The most common are ducks,
geese, pigeons and doves.
2.In 1993, Sec. of the Interior, Bruce
Babbitt launched a national
biological survey of wild species.
3. The 1975 CITES Treaty, Convention on International
Trade of Endangered Species, bans commercial trade
of an agreed list of endangered and threatened
species.
METHODS OF WILD
SPECIES PROTECTION
1. Ecosystem approach protects the whole
habitat
2. Species approach captivity breeding
3. Wildlife management may involve moving
species, regulating
hunting, harvesting
IMPROVING SURVIVAL
ODDS
1. Captive breeding programs
2. Egg pulling for relocation in a
safe place
3. Regulating hunting with
licenses and habitat
protection
4. Exclusive economic zones
for commercial fishing
5. Protection of migratory bird
flyways
6. Fishing quotas
7. Zoos currently only
house 27 endangered
populations of more
than 100 individuals,
but zoos also create
problems:
a. They have limited
space for larger
populations who need
greater habitat space.
b. Individuals can’t go
back home if their
habitat is gone.
c. Animals in zoos can’t
fulfill their roles in the
ecosystem.
4.6 MANATEES
MANATEE FACTS:
1. The Florida Manatee has been protected by state
law since 1893 and by the Endangered Species
Act of 1973 - but only about 3000 still survive.
2. Manatees are related to the elephant. There were 5
populations in the Order Sirenia.
a. West Indian Manatee - Trichechus manatus
migrates from Brazil to Florida
b. West African Manatee - coastal, freshwater of
Africa
c. Amazonian Manatee - freshwater in Amazon
basin
d. Dugong - found in Australia and Indonesia, has a
different tail
e. Stellar Sea Cow - hunted to extinction within 27
years of its discovery in 1741 in the Bering Strait
3. The average manatee is 10 feet and weighs 1000
pounds. Calves are around 4 feet and weigh 60
pounds.
4. They like warm, shallow water and need fresh water
to drink. Constant eating helps clear navigational
channels of water weeds.
5. In freshwater, they encounter boats where 50% of
their deaths are from human-related
FWS boat accidents.
6. Many manatees are identified by their boat propeller
FWS
scars.
7. Manatees are
herbivores, who eat 100
pounds of sea grass a
day or 10 % of their total
body weight.
8. They have large lips to
hold plants and
replaceable molars.
9. Because they have no
predators, no social
structure is present - not
territorial. Herds have no
leader and no permanent
bonds are formed for
mating.
MANATEE’S MAMMALIAN
CHARACTERISTICS
1.Whiskers (vibrissae) on the
snout are used to rake in plants
2.Mammary glands - cows nurse
their young for a year
3.Live births – the gestation
period is 13 months. They
produce one calf every 3-5 years
and don’t reach sexual maturity
until 5-9 years old
4.Warm-blooded with four
chambered heart
5.May live up to 60 years
6. Large brain - poor vision, hearing is primarily in a
different range from humans
7. Compartmentalized, ruminating stomach
8. Breathe air - may dive for 20 minutes
9. Marine mammal tail – horizontal paddle
10. Can produce a high-pitched whistle and clicks for
communication
4.7 Wildlife
Management
FWS
WILDLIFE MANAGEMENT OFFICER:
1. Manage sustainable biological resources is the
function of the wildlife officer.
2. These scientists manage the water, space, food and
shelter to benefit wild populations and enhance human
enjoyment of them.
3. The manager needs to know the habitat requirement of
the managed species, which can be grouped into 4
areas:
a. Early successional animals - those who require
weedy, pioneer plants in areas that have been
disturbed by fire, volcanoes, or human activity.
b. Mid-successional –
• Those who benefit from abandoned cropland and
open areas created by farming, logging, roadbuilding activities that create an edge effect.
• Edges, called ecotones, provide a transitional
zone for animals such as deer that feed in
clearings but can escape to the forest for cover.
c. Late-successional species - prefer old growth forests and
need larger spaces
d. Wilderness species - need undisturbed areas with mature
vegetation
5. Managers use techniques such as planting seeds,
clearing brush, building artificial nests, and
improving ponds to create and restore habitats.
GAME MANAGEMENT & HUNTERS
1. There is conflicting interest in the public between the
advantages of diversity vs. density.
2. Bird-watchers want diversity. Hunters want density.
3. Game animals are 10% of the wild species, but 90% of
the money spent on wildlife goes to this group.
4. Funds for state game management
come from the sale of hunting and
fishing licenses and from taxes on
hunting and fishing equipment.
5. There are over 16 million sports
hunters in the U.S. who contribute
significant money to support
research, and to buy, restore and
maintain wildlife habitats.
6. Without hunting season, some wild
species would exceed their carrying
capacity and starve.
7. Opponents say that wildlife
management creates a surplus of
game animals but not predators who
present a safety issue for humans
and livestock as well as reducing
game species.
FWS
8. Thinning populations is
then required because we
have altered the food
chain.
9. The Migratory Bird
Hunting and Conservation
Stamp Act (1934)
• requires duck stamps
FWS
for waterfowl hunters.
• The revenues are used
to buy and manage
their habitat.
GAME MANAGEMENT & FISHING
1. The fishing industry also has severe
management concerns.
2. Over-fishing has resulted from
enforcement issues, subsidies for
upgrading fishing fleet equipment, and
short-term economic needs.
3. Managers have tried to reduce overfishing by setting quotas, dividing the
allowable catch by the number of
commercial boats, and by regulating the
type of fish methods and gear.
4. Exclusive Economic Zone (EEZ)
• The area 200 nautical miles
off shore is the Exclusive
Economic Zone (EEZ) of the
adjacent country. Foreign
fleets are allowed only by
permission.
• However, beyond this legal
jurisdiction, usage of the high
seas is set by international
laws and treaties.
• Enforcement is very difficult
because if one fleet doesn’t
take the maximum catch,
someone else will. (Tragedy
of the Commons)
5. Sport-fishing is managed with
fishing licenses, seasons, quotas,
and the natural migration of fish.
6. Hatcheries and stocking programs
improve inland waters, but the high
seas are much more difficult.
7. The International Whaling
Commission is a good example of
interest in managing whale
populations after 8 of the 11 major
species were driven to commercial
extinction.
8. However, compliance is voluntary
and whales are no longer available.
The U.S. stopped whaling in 1970.